Re: [PATCH 1/4] hw/microblaze: Add endianness property to the petalogix_s3adsp1800 machine

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

+Markus

On 24/5/25 13:55, Richard Henderson wrote:
> On 5/15/25 14:20, Thomas Huth wrote:
>> +static int machine_get_endianness(Object *obj, Error **errp 
>> G_GNUC_UNUSED)
>> +{
>> +    S3Adsp1800MachineState *ms = PETALOGIX_S3ADSP1800_MACHINE(obj);
>> +    return ms->endianness;
>> +}
>> +
>> +static void machine_set_endianness(Object *obj, int endianness, Error 
>> **errp)
>> +{
>> +    S3Adsp1800MachineState *ms = PETALOGIX_S3ADSP1800_MACHINE(obj);
>> +    ms->endianness = endianness;
>> +}
>> +
>>   static void petalogix_s3adsp1800_machine_class_init(ObjectClass *oc,
>>                                                       const void *data)
>>   {
>>       MachineClass *mc = MACHINE_CLASS(oc);
>> +    ObjectProperty *prop;
>>       mc->desc = "PetaLogix linux refdesign for xilinx Spartan 
>> 3ADSP1800";
>>       mc->init = petalogix_s3adsp1800_init;
>>       mc->is_default = true;
>> +
>> +    prop = object_class_property_add_enum(oc, "endianness", 
>> "EndianMode",
>> +                                          &EndianMode_lookup,
>> +                                          machine_get_endianness,
>> +                                          machine_set_endianness);
>> +    object_property_set_default_str(prop, TARGET_BIG_ENDIAN ? "big" : 
>> "little");
>> +    object_class_property_set_description(oc, "endianness",
>> +            "Defines whether the machine runs in big or little endian 
>> mode");
> 
> 
> Better with Property?  You don't have to write get/set...
> 
>    static const Property props[] = {
>      DEFINE_PROP_ENDIAN("endianness", S3Adsp1800MachineState, endianness,
>                         TARGET_BIG_ENDIAN ? ENDIAN_MODE_BIG : 
> ENDIAN_MODE_LITTLE),
>    };
> 
>    device_class_set_props(dc, props);

DEFINE_PROP_FOO() are restricted to QDev (DeviceClass). Here we have
a MachineClass, which only inherits ObjectClass, not DeviceClass.

Markus once explained me the difference between QDev properties
and bare object ones; I asked why we couldn't make qdev properties
generic to objects, but I don't remember the historical rationale.
QDev predates QOM, QDev used static properties, QOM introduced
dynamic ones? We definitively should document that...